Add missing interface components

[devinamatthews]

• Library initialization (from TAPP_attr) (PR Fix destructors and add some constructors. #22)
• Executor initialization (also from TAPP_attr) (PR Fix destructors and add some constructors. #22)
• "bare" TAPP_attr initialization create/destroy (PR Fix destructors and add some constructors. #22)
• Reserved/assigned key/value IDs
• Documentation for key/value attributes
• Documentation for initialization (library and executor)